Golf ball layer having reduced surface hardness and method of making same

ABSTRACT

A golf ball comprising a core and a cover, wherein the core comprises a thermoset rubber composition, a geometric center and a treated outer surface, the treated outer surface having a first hardness and the geometric center having a second hardness, the treated outer surface being treated with a surface-softening material comprising at least one fatty acid and/or fatty acid salt plasticizer composition such that the second hardness is greater than the first hardness to define a negative hardness gradient. In another emobodiment, the golf ball comprises a thermoset rubber composition core and a cover, said core comprising a treated outer surface and a geometric center, the treated outer surface comprising a fatty acid and/or fatty acid salt plasticizer composition and extending inward from the surface from about 0.001 inches to about 0.100 inches, the treated outer surface further having a first hardness and the geometric center having a second hardness, wherein the first hardness is less than the second hardness to define a negative hardness gradient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 12/394,942, filed Feb. 27, 2009, which is acontinuation-in-part of co-pending U.S. patent application Ser. No.12/056,457, filed Mar. 27, 2008 which is a continuation of co-pendingU.S. patent application Ser. No. 12/048,665, filed Mar. 14, 2008, whichis a continuation-in-part of U.S. patent application Ser. No.11/772,903, filed Jul. 3, 2007, now U.S. Pat. No. 7,537,529. Thedisclosures of the parent cases are incorporated by reference herein intheir entireties.

FIELD OF THE INVENTION

This invention relates generally to golf balls with cores, moreparticularly either single layer cores or multilayer cores, having asurface hardness equal to or less than the center hardness.

BACKGROUND OF THE INVENTION

Solid golf balls are typically made with a solid core encased by acover, both of which can have multiple layers, such as a dual corehaving a solid center and an outer core layer, or a multi-layer coverhaving an inner and outer cover layer. Generally, golf ball cores and/orcenters are constructed with a thermoset rubber, typically apolybutadiene-based composition. The cores are usually heated andcrosslinked to create certain characteristics, such as higher or lowercompression, which can impact the spin rate of the ball and/or providebetter “feel.” These and other characteristics can be tailored to theneeds of golfers of different abilities. From the perspective of a golfball manufacturer, it is desirable to have cores exhibiting a wide rangeof properties, such as resilience, durability, spin, and “feel,” becausethis enables the manufacturer to make and sell many different types ofgolf balls suited to differing levels of ability.

Heretofore, most single core golf ball cores have had a conventionalhard-to-soft hardness gradient from the surface of the core to thecenter of the core. The patent literature contains a number ofreferences that discuss a hard surface to soft center hardness gradientacross a golf ball core.

U.S. Pat. No. 4,650,193 to Molitor et al. generally discloses a hardnessgradient in the surface layers of a core by surface treating a slug ofcurable elastomer with a cure-altering agent and subsequently moldingthe slug into a core. This treatment allegedly creates a core with twozones of different compositions, the first part being the hard,resilient, central portion of the core, which was left untreated, andthe second being the soft, deformable, outer layer of the core, whichwas treated by the cure-altering agent. The two “layers” or regions ofthe core are integral with one another and, as a result, achieve theeffect of a gradient of soft surface to hard center.

U.S. Pat. No. 3,784,209 to Berman, et al. generally discloses asoft-to-hard hardness gradient. The '209 patent discloses anon-homogenous, molded golf ball with a core of “mixed” elastomers. Acenter sphere of uncured elastomeric material is surrounded by acompatible but different uncured elastomer. When both layers ofelastomer are concurrently exposed to a curing agent, they becomeintegral with one another, thereby forming a mixed core. The center ofthis core, having a higher concentration of the first elastomericmaterial, is harder than the outer layer. One drawback to this method ofmanufacture is the time-consuming process of creating first elastomerand then a second elastomer and then molding the two together.

Other patents discuss cores that receive a surface treatment to providea soft ‘skin’. However, since the interior portions of these cores areuntreated, they have the similar hard surface to soft center gradient asconventional cores. For example, U.S. Pat. No. 6,113,831 to Nesbitt etal. generally discloses a conventional core and a separate soft skinwrapped around the core. This soft skin is created by exposing thepreform slug to steam during the molding process so that a maximum moldtemperature exceeds a steam set point, and by controlling exothermicmolding temperatures during molding. The skin comprises theradially-outermost 1/32 inch to ¼ inch of the spherical core. U.S. Pat.Nos. 5,976,443 and 5,733,206, both to Nesbitt et al., disclose theaddition of water mist to the outside surface of the slug before moldingin order to create a soft skin. The water allegedly softens thecompression of the core by retarding crosslinking on the core surface,thereby creating an even softer soft skin around the hard centralportion.

Additionally, a number of patents disclose multilayer golf ball cores,where each core layer has a different hardness thereby creating ahardness gradient from core layer to core layer.

There remains a need, however, to achieve an improved single layer corethat has a soft-to-hard gradient (a “negative” gradient), from thesurface to the center, and to achieve a method of producing such a corethat is inexpensive and efficient. A core exhibiting suchcharacteristics would allow the golf ball designer to create productswith unique combinations of compression, “feel,” and spin.

SUMMARY OF THE INVENTION

The present invention is directed to a method of making a golf ballcomprising the steps of providing an untreated golf ball core comprisinga thermoset rubber composition, the untreated golf ball core comprisingan untreated outer surface having a hardness; treating the untreatedouter surface of the untreated golf ball core with a surface-softeningmaterial comprising at least one fatty acid or fatty acid saltcomposition to form a golf ball core comprising a treated outer surfacehaving a hardness less than the hardness of the untreated outer surface;and forming at least one cover layer about the core to form the golfball.

Further, the present invention is directed to a method of making a golfball comprising the steps of providing an untreated golf ball corecomprising a thermoset rubber composition, said untreated golf ball corecomprising a geometric center and an untreated outer surface, eachhaving a hardness; treating the untreated golf ball core with asurface-softening material comprising at least one fatty acid or fattyacid salt composition to form a golf ball core comprising a treatedouter surface having a hardness less than the hardness of the untreatedouter surface, the treated outer surface further having a surfacehardness less than the hardness of the geometric center of the untreatedgolf ball core to define a negative hardness gradient; and forming acover layer about the core to form the golf ball.

In an alternative embodiment, the invention is directed to a method ofmaking a golf ball comprising the steps of providing a preformcomprising an uncured polybutadiene composition; coating the preformwith a first surface-softening material comprising at least one of afatty acid compound or a fatty acid salt compound; curing the coatedpreform at a predetermined temperature to form a crosslinked golf ballcore having an outer surface having a first hardness and a geometriccenter having a second hardness greater than the first to define anegative hardness gradient; and forming a cover layer about the core toform the golf ball.

Additionally, the present invention is directed to a method of making agolf ball comprising the steps of: extruding a polybutadiene compositionto form a cylindrical extrudate; cutting the extrudate to form anuncured polybutadiene preform; uniformly coating the preform with asurface-softening material comprising at least one fatty acid or fattyacid salt composition; curing the coated preform to form a crosslinkedcore having an outer surface having a first hardness and a geometriccenter having a second hardness greater than the first to define anegative hardness gradient; centerless-grinding the cured core to form auniformly-spherical core having increased surface roughness; forming aninner cover layer about the uniformly-spherical core; and forming anouter cover layer about the inner cover layer to form the golf ball.Alternatively, the golf ball comprises several layers which are treatedwith a surface-softening material comprising at least one fatty acid orfatty acid salt composition or blends/combinations thereof.

The present invention is also directed to a golf ball comprising a coreand a cover, wherein the core has an outer surface that is treated witha surface-softening material comprising at least one fatty acid or fattyacid salt composition such that the outer surface has a hardness ratio(R) of the hardness after treatment (H₂) to the hardness beforetreatment (H₁) of less than about 0.95.

The invention is further directed to a golf ball comprising a core and acover, wherein the core has a geometric center having a hardness (H_(g))and the core has an outer surface that is treated with asurface-softening material comprising at least one fatty acid or fattyacid salt composition such that the outer surface has an extrapolatedhardness (H_(E)) and an actual hardness (H_(OS)) wherein H_(E) isderived from a five point extrapolation within three quarters of anouter core diameter and H_(OS) is measured on the curved surface of thecore, and the cover has a hardness (H_(C)), whereinH_(C)>H_(E)>H_(g)>H_(OS).

In still another embodiment, a golf ball comprises a core and a cover,wherein the core has a geometric center having a hardness (H_(g)) andthe core has an outer surface that is treated with at least one fattyacid or fatty acid salt such that the outer surface has an extrapolatedhardness (H_(E)) and an actual hardness (H_(OS)) wherein H_(E) isderived from a five point extrapolation within three quarters of anouter core diameter and H_(OS) is measured on the curved surface of thecore, and the cover has a hardness (H_(C)), whereinH_(E)>H_(g)>H_(OS)>H_(C).

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to methods for treating golf ballcores to reduce core surface hardness, and to golf balls having reducedsurface hardness. In a first embodiment, an untreated thermoset rubbergolf ball core comprising an untreated outer surface having an untreatedsurface hardness, is treated with a surface-softening materialcomprising at least one fatty acid or fatty acid salt composition. Theresulting treated golf ball core comprises a treated outer surfacehaving a hardness which is less than the hardness of the untreated outersurface. Then, at least one cover layer is formed about the treated coreto form the golf ball.

The thermoset rubber composition may comprise, for example,polybutadiene compositions as discussed herein. The terms thermosetrubber, cured rubber, and crosslinked rubber are used interchangeablyherein, and all refer to a diene rubber composition which has undergoneat least some degree of polymerization.

The step of treating typically includes but is not limited to coating,rolling, dipping, soaking, spraying, dusting, or exposing the untreatedgolf ball core to at least one fatty acid or fatty acid salt compositionor blends/combinations thereof.

The at least one fatty acid or fatty acid salt composition may include,for example, oleic acid, palmitic acid, stearic acid, behenic acid,pelargonic acid, linoleic acid, linolenic acid, arachidonic acid,caproic acid, caprylic acid, capric acid, lauric acid, erucic acid,myristic acid, benzoic acid, phenylacetic acid, or naphthalenoic acid.The at least one fatty acid or fatty acid salt composition may furtherinclude antioxidants, sulfur-bearing compounds, zinc methacrylate, zincdimethacrylate, softening acrylate monomers or oligomers, soft powderedthermoplastic resins, phenol-comprising antioxidants, or hydroquinones.

The untreated golf ball core may also include other compositions formodifying the properties of the core surface, such as thermoplasticelastomers and other polymers, also discussed herein.

In addition, the step of treating the untreated core with the fatty acidor fatty acid salt composition or blends/combinations of the presentinvention may be followed by a subsequent step of neutralizing thetreated core/preform surface, either partially or fully, with a cationor other suitable source. Suitable cation sources include but are notlimited to barium, lithium, sodium, zinc, bismuth, chromium, cobalt,copper, potassium, strontium, titanium, tungsten, magnesium, cesium,iron, nickel, silver, aluminum, tin and calcium.

In a further embodiment, an untreated crosslinked golf ball corecomprising a thermoset rubber composition has a geometric center and anuntreated outer surface, each having a hardness. The untreatedcrosslinked golf ball core is treated with a surface-softening materialcomprising at least one fatty acid or fatty acid salt composition. Agolf ball core is then formed comprising a treated outer surface havinga hardness less than the hardness of the untreated outer surface. Thetreated outer surface may further have a surface hardness less than thehardness of the geometric center of the untreated golf ball core todefine a negative hardness gradient. Then, a cover layer is formed aboutthe core to form the golf ball.

In an alternative embodiment, a preform comprising an uncuredpolybutadiene composition is coated with a first surface-softeningmaterial comprising at least one of a fatty acid compound or a fattyacid salt compound. Following treatment with the fatty acid and/or fattyacid salt compositions, the uncured treated golf ball core material maybe compression molded at a predetermined temperature for a predeterminedtime, e.g. 330-360° F. for 11 minutes to form a molded core. Acrosslinked golf ball core is thus formed having an outer surface havinga first hardness and a geometric center having a second hardness greaterthan the first to define a negative hardness gradient. Then, optionally,the molded core may also be subjected to Gleber or centerless grinding.A cover layer is then formed about the core to form the golf ball.

In another embodiment, a polybutadiene composition is extruded to form acylindrical extrudate and the extrudate is cut to form an uncuredpolybutadiene perform. The perform is then cold formed into a sphere,and uniformly coated with a surface-softening material comprising atleast one fatty acid and/or fatty acid salt composition. In a preferredembodiment, the perform is subjected to centerless grinding prior to thetreating step. The core may also be preheated to a predeterminedtemperature followed by treatment with the fatty acid and/or fatty acidsalt composition. The coated preform is then cured to form a crosslinkedcore having an outer surface having a first hardness and a geometriccenter having a second hardness greater than the first to define anegative hardness gradient. In an alternative embodiment, the cured coreis subsequently subjected to center-less grinding to form auniformly-spherical core having increased surface roughness, an innercover layer is formed about the uniformly-spherical core, and an outercover layer is formed about the inner cover layer to form the golf ball.The core may also alternatively be heated at a predetermined temperaturefor a predetermined time following treatment with the fatty acid/fattyacid salt composition.

In one embodiment, the thermoset rubber composition core is partiallycured before the step of treating the core with the surface-softeningmaterials of the present invention. Following treatment, the treatedcore is subjected to conditions, for example, heat, in order to affectadditional curing or crosslinking. Additionally, the golf ball core maycomprise several layers which are treated with a surface-softeningmaterial comprising at least one fatty acid or fatty acid saltcomposition or blends/combinations thereof.

In one embodiment, a golf ball comprises a core and a cover, wherein thecore has an outer surface that is treated with at least one fatty acidsuch that the outer surface has a hardness ratio (R) of the hardnessafter treatment (H₂) to the hardness before treatment (H₁) of less thanabout 0.95.

In yet another embodiment, a golf ball comprises a core and a cover,wherein the core has a geometric center having a hardness (H_(g)) andthe core has an outer surface that is treated with at least one fattyacid or fatty acid salt such that the outer surface has an extrapolatedhardness (H_(E)) and an actual hardness (H_(OS)) wherein H_(E) isderived from a five point extrapolation within three quarters of anouter core diameter and H_(OS) is measured on the curved surface of thecore, and the cover has a hardness (H_(C)), whereinH_(E)>H_(g)>H_(OS)>H_(C).

In still another embodiment, a golf ball comprises a core and a cover,wherein the core has a geometric center having a hardness (H_(g)) andthe core has an outer surface that is treated with at least one fattyacid or fatty acid salt such that the outer surface has an extrapolatedhardness (H_(E)) and an actual hardness (H_(OS)) wherein H_(E) isderived from a five point extrapolation within three quarters of anouter core diameter and H_(OS) is measured on the curved surface of thecore, and the cover has a hardness (H_(C)), whereinH_(E)>H_(g)>H_(OS)>H_(C).

The balls of the present invention may include a single-layer(one-piece) golf ball, two-piece golf ball (core and cover) andmulti-layer or multi-piece golf balls, such as one having a core of oneor more layers and a cover of one or more layers surrounding the core,but are preferably formed from a core comprised of a solid center(otherwise known as an inner core) and an outer core layer, an innercover layer and an outer cover layer. Of course, any of the core and/orthe cover layers may include more than one layer. In a preferredembodiment, the core is formed of an inner core and an outer core layerwhere both the inner core and the outer core layer have a “soft-to-hard”hardness gradient (a “negative” hardness gradient) radially inward fromeach component's outer surface towards its innermost portion (i.e., thecenter of the inner core or the inner surface of the outer core layer),although alternative embodiments involving varying direction andcombination of hardness gradient amongst core components are alsoenvisioned (e.g., a “negative” gradient in the center coupled with a“positive” gradient in the outer core layer, or vice versa).

The center of the core may also be a liquid-filled or hollow spheresurrounded by one or more intermediate and/or cover layers, or it mayinclude a solid or liquid center around which tensioned elastomericmaterial is wound. Any layers disposed around these alternative centersmay exhibit the inventive core surface-softening. The cover layer may bea single layer or, for example, formed of a plurality of layers, such asan inner cover layer and an outer cover layer.

As briefly discussed above, the inventive cores may have a hardnessgradient defined by hardness measurements made at the surface of theinner core (or outer core layer) and radially inward toward the centerof the inner core, typically at 2-mm increments. As used herein, theterms “negative” and “positive” refer to the result of subtracting thehardness value at the innermost portion of the component being measured(e.g., the center of a solid core or an inner core in a dual coreconstruction; the inner surface of a core layer; etc.) from the hardnessvalue at the outer surface of the component being measured (e.g., theouter surface of a solid core; the outer surface of an inner core in adual core; the outer surface of an outer core layer in a dual core,etc.). For example, if the outer surface of a solid core has a lowerhardness value than the center (i.e., the surface is softer than thecenter), the hardness gradient will be deemed a “negative” gradient (asmaller number−a larger number=a negative number). It is preferred thatthe inventive cores have a zero or a negative hardness gradient. In oneembodiment, the hardness of the treated outer surface is at least 5Shore C less than the hardness of the untreated golf ball core surface.In another embodiment, the hardness of the treated outer surface is atleast 10 Shore C less than the hardness of the untreated golf ball coresurface. In a preferred “negative” gradient embodiment, the core outersurface hardness is lower than the core geometric center hardness byabout 0 to 30 Shore C, more preferably by about 5 to 25 Shore C lower,and at most the core outer surface hardness is about 8 to 20 Shore Clower than the core geometric center hardness.

The invention is more particularly directed to the creation of a soft“skin” on the outermost surface of the core, such as the outer surfaceof a single core or the outer surface of the outer core layer in a dualcore construction. The “skin” is typically defined as the volume of thecore that is within about 0.001 inches to about 0.100 inches of thesurface, and more preferably about 0.003 inches to about 0.050 inches.Alternatively, the volume may be within 0.005 inches to about 0.030inches of the surface. In one embodiment, a single or multi-layer coreis treated as a preform (prior to molding) by coating the surface of thepreform with a surface-softening material.

The surface-softening material may be in a solid form, typically apowder, prill, gaseous or small pellet, but alternatively may be insolution form, such as a liquid, dispersion, or slurry in a solvent.Suitable solvents or carriers include, but are not limited to, water,hydrocarbon solvents, polar solvents, and plasticizers. If a liquid isused, it is preferably one that dissolves the fatty acid. Mostpreferably, the surface-softening material is a liquid at or near roomtemperature and requires no solvent.

Preferably, the layer to be treated with the surface-softening materialis a core or core layer, but also in an alternative embodiment the layeris a cover or cover layer (inner or outer cover layer) comprising adiene rubber composition, preferably polybutadiene rubber.

In a preferred embodiment, the golf ball core surface or preform iscoated by rolling, dipping, soaking, spraying, dusting, or otherwiseexposing the core surface to at least one surface-softening materialcomprising at least one fatty acid or fatty acid salt composition orblends/combinations thereof.

Suitable fatty acids include but are not limited to oleic acid, palmiticacid, stearic acid, behenic acid, pelargonic acid, linoleic acid,linolenic acid, arachidonic acid, caproic acid, caprylic acid, capricacid, lauric acid, erucic acid, myristic acid, benzoic acid,phenylacetic acid, naphthalenoic acid, dimerized derivatives thereof,salts, cation, blends and combinations thereof. Certain fatty acids suchas oleic acid, linoleic acid, linolenic acid, arachidonic acid areparticularly suitable because they are in liquid form at roomtemperature and the core can therefore be easily immersed/dipped in theneat material. Such fatty acids include, for example, oleic acid,linoleic acid, linolenic acid and arachidonic acid.

Suitable fatty acid cations include, for example, barium, lithium,sodium, zinc, bismuth, chromium, cobalt, copper, potassium, strontium,titanium, tungsten, magnesium, cesium, iron, nickel, silver, aluminum,tin and calcium.

Additional suitable surface-softening and/or cure-altering materials maybe either combined directly with the fatty acid or fatty acid saltcomposition and blends/combinations and/or used to pretreat the preformprior to coating the perform with the fatty acid fatty acid saltcompositions. Examples include, but are not limited to, antioxidants,sulfur-bearing compounds such as pentachlorothiophenol or metal saltsthereof, ZDMA, softening acrylate monomers or oligomers, and softpowdered thermoplastic resins such as ethyl vinyl acetate, ethylenebutyl acrylate, ethylene methyl acrylate, and very-low-modulus ionomers.Preferred additional surface softening materials include, for example,phenol-comprising antioxidants, hydroquinones, and “soft and fast”agents, such as organosulfur compounds, inorganic sulfur compounds, andthiophenols, particularly pentachlorothiophenol (PCTP) and metal saltsof PCTP, such as ZnPCTP, MgPCTP, DTDS, and those disclosed in U.S. Pat.Nos. 6,458,895; 6,417,278; and 6,635,716; and U.S. Patent ApplicationPublication Serial No. 2006/021586, the disclosures of which areincorporated herein by reference. Alternatively, thermoplastic orthermosetting powders, such as low molecular weight polyethylene, ethylvinyl acetate, ethylene copolymers and terpolymers (i.e., NUCREL®),ethylene butyl acrylate, ethylene methyl acrylate, polyurethanes,polyureas, polyurethane-copolymers (i.e., silicone-urethanes), PEBAX®,HYTREL®, polyesters, polyamides, epoxies, silicones, and Micromorph®materials, such as those disclosed in U.S. patent applicationPublication Ser. Nos. 11/690,530 and 11/690,391, incorporated herein byreference.

In one particularly preferred embodiment, a polybutadiene rubber preformis coated with an antioxidant-comprising powder and then molded at350-360° F. for 11 minutes to form a single core. The resultant core hasan outer diameter of about 1.580 inches and a geometric center-pointhardness of about 60 to 80 Shore C, preferably about 65 to 78 Shore C,and most preferably about 70 to 75 Shore C. At a point about 15 mm toabout 20 mm from the center point of the core, the soft “skin” has ahardness of about 60 to 80 Shore C, preferably about 65 to 75 Shore C,and most preferably about 68 to 74 Shore C, resulting in an overallgradient (as measured from center to surface) of zero, and mostpreferably negative (i.e., about −30 to 0, more preferably about −15 to0, most preferably about −10 to 0). The core of this example typicallyhas an Atti compression of about 70 and a COR of about 0.800, whenmeasured at an incoming velocity of 125 ft/s. Preferred Atti corecompressions are 110 of less, preferably 100 or less, more preferably 90or less, and most preferably 80 or less.

A second particularly preferred embodiment is a two-piece core formedfrom an inner core and an outer core layer. The inner core may or maynot be “treated” as described herein, but preferably the outer corelayer is treated to create the soft outer “skin.” In one embodiment, asoft inner core is surrounded by a relatively hard outer core layer. Theinner core preferably has a an outer diameter of about 1.0 inch, acenter point hardness of about 55 to 60 Shore C, and an outer surfacehardness of about 75 to 80 Shore C. The surface hardness of the modified“skin” of the outer core layer is about 60 to 80 Shore C, morepreferably about 65 to 75 Shore C, and most preferably about 68 to 74Shore C. A preferred overall gradient is negative to zero, mostpreferably negative (i.e., about −30 to 0, more preferably about −20 to−3, and most preferably about −15 to −5).

The core formulations used in the invention are preferably based uponhigh-cis polybutadiene rubber that is cobalt-, nickel-, lithium-, orneodymium-catalyzed, most preferably Co- or Nd-catalyzed, having aMooney viscosity of about 25 to about 125, more preferably about 30 toabout 100, and most preferably about 40 to about 60. Lesser amounts ofnon-polybutadiene rubber, such as styrene butadiene rubber,trans-polyisoprene, natural rubber, butyl rubber, ethylene propylenerubber, ethylene propylene diene monomer rubber, low-cis polybutadienerubber, or trans polybutadiene rubber, may also be blended with thepolybutadiene rubber. A coagent, such as zinc diacrylate or zincdimethacrylate, is typically present at a level of about 0 pph to about60 pph, more preferably about 10 pph to about 55 pph, and mostpreferably about 15 pph to about 40 pph. A peroxide or peroxide blend isalso typically present at about 0.1 pph to about 5.0 pph, morepreferably about 0.5 pph to about 3.0 pph. Zinc oxide may also bepresent at about 2 pph to about 50 pph and the antioxidant is preferablypresent at about 0 pph to about 5.0 pph, preferably about 0.5 pph toabout 3.0 pph. Elemental sulfur may also be present in the amount ofabout 0.05 to 2 pph, preferably about 0.1 to 0.5 pph.

Other embodiments include any number of core layers and gradientcombinations wherein at least one layer of the core has a surface thatis “treated” as described herein.

Scrap automotive tire regrind (in fine powder form) is also sufficientfor creating the inventive soft outer “skin,” as well as other powderedrubbers that are uncrosslinked or partially crosslinked and thereforeable to react with the polybutadiene. Fully crosslinked powdered rubbermay also still have enough affinity for the polybutadiene substrate toadhere (even react minimally) enough to form a good bond.

The inner and outer core formulations may comprise a diene rubber, acure initiator, and a coagent. Suitable diene rubbers include, forexample, those disclosed in U.S. patent application Ser. No. 11/561,923('923 application), incorporated herein by reference. Suitable cureinitiators include for example, peroxide or sulfur. The coagent maycomprise ZDA, ZDMA, TMPTA, HVA-2 or any of those identified in the '923application. Optionally, the formulations may also include one or moreof a zinc oxide, zinc stearate or stearic acid, antioxidant, or soft tofast agent such as PCTP or ZnPCTP. Either the inner or outer core, morepreferably the outer core, may further comprise from about 1 to 100 phrof a stiffening or toughening thermoplastic polymer such as an ionomer,an acid co- or ter-polymer, polyamide, polyester or any as disclosed inU.S. Pat. No. 6,120,390 or 6,284,840, incorporated herein by reference.Preferably, the inner and outer core layers comprise a highcis-neodymium catalyzed polybutadiene such as Neodene 40 or CB-23, or acobalt or nickel or lithium catalyzed PBR such as BR-1220 or BR-221. Atrans PIP, for example balata TP-301, or trans BR may be used to addstiffness to the cores and/or improve cold forming properties,particularly for ease of molding a half-shell for the outer coreformation.

Other potential surface-softening or cure-altering agents include, butare not limited to, sulfated fats, sodium salts of alkylated aromaticsulfonic acids, substituted benzoid alkyl sulfonic acids, monoaryl andalkyl ethers of diethylene glycol and dipropylene glycol, ammonium saltsof alkyl phosphates, sodium alkyl sulfates and monosodium salt ofsulfated methyl oleate and sodium salts of carboxylated electrolytes.Other suitable materials include dithiocarbamates, such as zinc dimethyldithiocarbamate, zinc diethyl dithiocarbamate, zinc di-n-butyldithiocarbamate, zinc diamyl dithiocarbamate, tellurium diethyldithiocarbamate, selenium dimethyl dithiocarbamate, selenium diethyldithiocarbamate, lead diamyl dithiocarbamate, bismuth dimethyldithiocarbamate, cadmium diethyl dithiocarbamate, and mixtures thereof.

The method for making the golf ball of the invention includes a varietyof steps and options. Typically, a Banbury-type mixer or the like isused to mix the polybutadiene rubber composition. The rubber compositionis extruded as an extrudate and cut to a predetermined shape, such as acylinder, typically called a “preform”. The preform comprising theuncured polybutadiene composition is then prepared for coating with atleast one of the surface-softening (inhibiting) materials, liquids, orsolvents described above. Other surface-softening and/or cure-alteringmaterials may be added for coating, comprising antioxidants,sulfur-bearing compounds, zinc methacrylate, zinc dimethacrylate,softening acrylate monomers or oligomers, soft powdered thermoplasticresins, phenol-comprising antioxidants, or hydroquinones, mostpreferably an antioxidant.

In one embodiment, more than one surface-softening material is used, insuccession. In this embodiment, a preferred combination includes a firstsurface-softening material in combination with a cure-altering materialsuch as an antioxidant and a second cure-altering material such as adifferent antioxidant or a peroxide. A compatibilizer and/or tie layermay be incorporated as well. Additionally, a two-stage dip or roll (inthe cure-altering material) may be used to sequentially also provide afirst and second antioxidant or an antioxidant and a peroxide inaddition to providing the fatty acid and/or fatty acid salt composition.

Optionally, prior to coating the preform, the uncured preform may beshaped or cold-formed into a rough sphere. The coating may be performedin a variety of manners including, but not limited to, rolling,spraying, dipping, or dusting or otherwise exposing. The coating may beuniform or varied, but is preferably uniform.

The uncured, coated preform may optionally be heated to a predeterminedtemperature for a predetermined time, the temperature beingsubstantially below the predetermined cure temperature, so that thecure-altering material may diffuse, penetrate, migrate, or otherwisework its way into the preform or, alternatively, any solvent mayevaporate or the preform may dry (if the coating was in liquid form).Where two surface-softening materials are employed in a coating, or inthe case where a surface-softening material is used in combination witha cure-altering material as the coating material, the predetermined timemay also be set in order to allow any reaction that may occur to come tocompletion.

The uncured coated preform is then cured or molded at a predeterminedtemperature and time to form a crosslinked golf ball core. As describedin detail above, the core has an outer surface having a first hardnessand a geometric center having a second hardness greater than the firstto define a “negative” hardness gradient. Any one of a number of coverlayers may be formed around the “negative” gradient core including, butnot limited to, an outer core layer, an inner cover layer, and an outercover layer.

The cured core is then typically subjected to centerless-grinding sothat the core is uniformly spherical and has a surface than is roughenedand textured to be better suited for adhesion with subsequent layers.Prior to or after the centerless grinding, the core may be treated withplasma discharge, corona discharge, silanes, or chlorination, forexample, to aid in its adhesion properties.

In a preferred embodiment, a thermoset rubber core is soaked in a liquidfatty acid composition including, for example, oleic acid. Following thesoaking step, the core is removed from the surface-softening compositionand wiped dry in order to remove any excess oleic acid. A cover layer isthen molded over the treated core. Preferably, the surface hardness isreduced from about 85 Shore C to about 83 Shore C or less, and morepreferably, to about 80 Shore C or less. In one embodiment, a negativegradient may be created if the Shore C surface hardness after treatmentis about 60 Shore C or less and the center hardness is about 62 Shore C.The degree of resulting core surface softness is directly related to theduration of core surface exposure to the surface-softening compositionso that a particular resulting core surface hardness may be achieved byvarying the duration of exposure.

Alternatively, the fatty acid may comprise a heated molten form ofmagnesium oleate. Additionally, the core may be exposed i.e., dipped orsoaked, in a solvent solution of stearic acid and zinc oxide intetrahydrofuran (THF).

In one embodiment, the untreated thermoset rubber golf ball core has anouter diameter of 1.400-1.640 inches, and more preferably 1.50-1.62inches, and most preferably 1.55-1.60 inches. Additionally, thethermoset rubber golf ball core has a compression of about 30-120, andmore preferably 40-110, and most preferably 60-105. Further, theuntreated core has a Shore C surface hardness of about 50-95, or morepreferably about 60-93 Shore C, and most preferably in the range ofabout 75-89 Shore C. The core is dipped in oleic acid at a temperatureof about 40-350° F. for a time of about 1 second to about 24 hours. Morepreferably, the temperature and duration is 50-150° F. for about 1minute to about 12 hours. Most preferably, the temperature and durationare about 60-110° F. for about 5 minutes to about 6 hours, respectively.The resulting treated core has a surface hardness of about 1 to 50 ShoreC lower than the surface hardness of the untreated core, or morepreferably about 5 to 25 Shore C lower, and most preferably about 10 to20 Shore C lower.

One embodiment includes the steps of extruding a polybutadienecomposition to form a cylindrical extrudate; cutting the extrudate toform an uncured polybutadiene preform; uniformly coating the preformwith a cure-altering material comprising a first antioxidant; curing thecoated preform to form a crosslinked core having an outer surface havinga first hardness and a geometric center having a second hardness greaterthan the first to define a negative hardness gradient;centerless-grinding the cured core to form a uniformly-spherical corehaving increased surface roughness; forming an inner cover layer aboutthe uniformly-spherical core; and forming an outer cover layer about theinner cover layer to form the golf ball.

In yet another embodiment, a thermoset rubber or at least partiallycured diene rubber composition is ground, pulverized or otherwiseconverted into the form of a particle having a regular or irregularshape and a particle size of from about 1 nm to about 2 mm in diameter(or maximum cross sectional length). The ground thermoset rubber may beformed by grinding a thermoset golf ball core to a sieve size of about10-40 mesh. Such a ground golf ball core is commonly referred to as golfball core regrind. The ground thermoset rubber is then treated with afatty acid or fatty acid salt comprising composition to soften at leastthe surface of the ground particle. The treated ground thermoset rubberparticles are then admixed with an uncured diene rubber compositionfollowed by the steps needed to form a golf ball core, ie extrusion,forming a perform, crosslinking into a spherical core, etc. The additionof the treated ground thermoset rubber to the diene rubber compositionis meant to soften and perhaps enhance the feel of the molded corecomprising the treated ground rubber, and lower core compression whilehaving little adverse effect on core speed.

Preferably, the core layers (inner core or outer core layer) is madefrom a composition including at least one thermoset base rubber, such asa polybutadiene rubber, cured with at least one peroxide and at leastone reactive co-agent, which can be a metal salt of an unsaturatedcarboxylic acid, such as acrylic acid or methacrylic acid, anon-metallic coagent, or mixtures thereof. Preferably, a suitableantioxidant is included in the composition. An optional soft and fastagent (and sometimes a cis-to-trans catalyst), such as an organosulfuror metal-containing organosulfur compound, can also be included in thecore formulation

Other ingredients that are known to those skilled in the art may beused, and are understood to include, but not be limited to,density-adjusting fillers, process aides, plasticizers, blowing orfoaming agents, sulfur accelerators, and/or non-peroxide radicalsources.

The base thermoset rubber, which can be blended with other rubbers andpolymers, typically includes a natural or synthetic rubber. A preferredbase rubber is 1,4-polybutadiene having a cis structure of at least 40%,preferably greater than 80%, and more preferably greater than 90%.

Examples of desirable polybutadiene rubbers include BUNA® CB22 and BUNA®CB23, commercially available from LANXESS Corporation; UBEPOL® 360L andUBEPOL® 150L and UBEPOL-BR rubbers, commercially available from UBEIndustries, Ltd. of Tokyo, Japan; KINEX® 7245 and KINEX® 7265,commercially available from Goodyear of Akron, Ohio; Shell BR-1220,commercially available from Dow chemical Company, Europrene® NEOCIS® BR40 and BR 60, commercially available from Polimeri Europa; and BR 01, BR730, BR 735, BR 11, and BR 51, commercially available from JapanSynthetic Rubber Co., Ltd; PETROFLEX® BRNd-40; and KARBOCHEM® ND40,ND45, and ND60, commercially available from Karbochem.

The base rubber may also comprise high or medium Mooney viscosityrubber, or blends thereof. A “Mooney” unit is a unit used to measure theplasticity of raw or unvulcanized rubber. The plasticity in a “Mooney”unit is equal to the torque, measured on an arbitrary scale, on a diskin a vessel that contains rubber at a temperature of 100° C. and rotatesat two revolutions per minute. The measurement of Mooney viscosity isdefined according to ASTM D-1646.

The Mooney viscosity range is preferably greater than about 40, morepreferably in the range from about 40 to about 80 and more preferably inthe range from about 40 to about 60. Polybutadiene rubber with higherMooney viscosity may also be used, so long as the viscosity of thepolybutadiene does not reach a level where the high viscositypolybutadiene clogs or otherwise adversely interferes with themanufacturing machinery. It is contemplated that polybutadiene withviscosity less than 65 Mooney can be used with the present invention.

In one embodiment of the present invention, golf ball cores made withmid- to high-Mooney viscosity polybutadiene material exhibit increasedresiliency (and, therefore, distance) without increasing the hardness ofthe ball. Such cores are soft, i.e., compression less than about 60 andmore specifically in the range of about 50-55. Cores with compression inthe range of from about 30 about 50 are also within the range of thispreferred embodiment.

Commercial sources of suitable mid- to high-Mooney viscositypolybutadiene include Bayer AG CB23 (Nd-catalyzed), which has a Mooneyviscosity of around 50 and is a highly linear polybutadiene, and Shell1220 (Co-catalyzed). If desired, the polybutadiene can also be mixedwith other elastomers known in the art, such as other polybutadienerubbers, natural rubber, styrene butadiene rubber, and/or isoprenerubber in order to further modify the properties of the core. When amixture of elastomers is used, the amounts of other constituents in thecore composition are typically based on 100 parts by weight of the totalelastomer mixture.

In one preferred embodiment, the base rubber comprises a Nd-catalyzedpolybutadiene, a rare earth-catalyzed polybutadiene rubber, or blendsthereof. If desired, the polybutadiene can also be mixed with otherelastomers known in the art such as natural rubber, polyisoprene rubberand/or styrene-butadiene rubber in order to modify the properties of thecore. Other suitable base rubbers include thermosetting materials suchas, ethylene propylene diene monomer rubber, ethylene propylene rubber,butyl rubber, halobutyl rubber, hydrogenated nitrile butadiene rubber,nitrile rubber, and silicone rubber.

Thermoplastic elastomers (TPE) many also be used to modify theproperties of the core layers, or the uncured core layer stock byblending with the base thermoset rubber. These TPEs include natural orsynthetic balata, or high trans-polyisoprene, high trans-polybutadiene,or any styrenic block copolymer, such as styrene ethylene butadienestyrene, styrene-isoprene-styrene, etc., a metallocene or othersingle-site catalyzed polyolefin such as ethylene-octene, orethylene-butene, or thermoplastic polyurethanes (TPU), includingcopolymers, e.g. with silicone. Other suitable TPEs for blending withthe thermoset rubbers of the present invention include PEBAX®, which isbelieved to comprise polyether amide copolymers, HYTREL®, which isbelieved to comprise polyether ester copolymers, thermoplastic urethane,and KRATON®, which is believed to comprise styrenic block copolymerselastomers. Any of the TPEs or TPUs above may also contain functionalitysuitable for grafting, including maleic acid or maleic anhydride.

Suitable peroxide initiating agents include dicumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy) hexane;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne;2,5-dimethyl-2,5-di(benzoylperoxy)hexane;2,2′-bis(t-butylperoxy)-di-iso-propylbenzene;1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane; n-butyl4,4-bis(t-butyl-peroxy)valerate; t-butyl perbenzoate; benzoyl peroxide;n-butyl 4,4′-bis(butylperoxy)valerate; di-t-butyl peroxide; or2,5-di-(t-butylperoxy)-2,5-dimethyl hexane, lauryl peroxide, t-butylhydroperoxide, α-α bis(t-butylperoxy) diisopropylbenzene,di(2-t-butyl-peroxyisopropyl)benzene, di-t-amyl peroxide, di-t-butylperoxide. Preferably, the rubber composition includes from about 0.25 toabout 5.0 parts by weight peroxide per 100 parts by weight rubber (phr),more preferably 0.5 phr to 3 phr, most preferably 0.5 phr to 1.5 phr. Ina most preferred embodiment, the peroxide is present in an amount ofabout 0.8 phr. These ranges of peroxide are given assuming the peroxideis 100% active, without accounting for any carrier that might bepresent. Because many commercially available peroxides are sold alongwith a carrier compound, the actual amount of active peroxide presentmust be calculated. Commercially-available peroxide initiating agentsinclude DICUP™ family of dicumyl peroxides (including DICUP™ R, DICUP™40C and DICUP™ 40KE) available from Crompton (Geo Specialty Chemicals).Similar initiating agents are available from AkroChem, Lanxess,Flexsys/Harwick and R.T. Vanderbilt. Another commercially-available andpreferred initiating agent is TRIGONOX™ 265-50B from Akzo Nobel, whichis a mixture of 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane anddi(2-t-butylperoxyisopropyl) benzene. TRIGONOX™ peroxides are generallysold on a carrier compound.

Suitable reactive co-agents include, but are not limited to, metal saltsof diacrylates, dimethacrylates, and monomethacrylates suitable for usein this invention include those wherein the metal is zinc, magnesium,calcium, barium, tin, aluminum, lithium, sodium, potassium, iron,zirconium, and bismuth. Zinc diacrylate (ZDA) is preferred, but thepresent invention is not limited thereto. ZDA provides golf balls with ahigh initial velocity. The ZDA can be of various grades of purity. Forthe purposes of this invention, the lower the quantity of zinc stearatepresent in the ZDA the higher the ZDA purity. ZDA containing less thanabout 10% zinc stearate is preferable. More preferable is ZDA containingabout 4-8% zinc stearate. Suitable, commercially available zincdiacrylates include those from Sartomer Co. The preferred concentrationsof ZDA that can be used are about 10 phr to about 40 phr, morepreferably 20 phr to about 35 phr, most preferably 25 phr to about 35phr. In a particularly preferred embodiment, the reactive co-agent ispresent in an amount of about 29 phr to about 31 phr.

Additional preferred co-agents that may be used alone or in combinationwith those mentioned above include, but are not limited to,trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, andthe like. It is understood by those skilled in the alt, that in the casewhere these co-agents may be liquids at room temperature, it may beadvantageous to disperse these compounds on a suitable carrier topromote ease of incorporation in the rubber mixture.

Antioxidants are compounds that inhibit or prevent the oxidativebreakdown of elastomers, and/or inhibit or prevent reactions that arepromoted by oxygen radicals. Some exemplary antioxidants that may beused in the present invention include, but are not limited to, quinolinetype antioxidants, amine type antioxidants, and phenolic typeantioxidants. A preferred antioxidant is2,2′-methylene-bis-(4-methyl-6-t-butylphenol) available as VANOX® MBPCfrom R.T. Vanderbilt. Other polyphenolic antioxidants include VANOX® T,VANOX® L, VANOX® SKT, VANOX® SWP, VANOX® 13 and VANOX® 1290.

The antioxidant is typically present in an amount of about 0.1 phr toabout 5 phr, preferably from about 0.1 phr to about 2 phr, morepreferably about 0.1 phr to about 1 phr. In a particularly preferredembodiment, the antioxidant is present in an amount of about 0.4 phr. Inan alternative embodiment, the antioxidant should be present in anamount to ensure that the hardness gradient of the inventive cores isnegative. Preferably, about 0.2 phr to about 1 phr antioxidant is addedto the core layer (inner core or outer core layer) formulation, morepreferably, about 0.3 to about 0.8 phr, and most preferably 0.4 to about0.7 phr. Preferably, about 0.25 phr to about 1.5 phr of peroxide ascalculated at 100% active can be added to the core formulation, morepreferably about 0.5 phr to about 1.2 phr, and most preferably about 0.7phr to about 1.0 phr. The ZDA amount can be varied to suit the desiredcompression, spin and feel of the resulting golf ball. The cure regimecan have a temperature range between from about 290° F. to about 400°F., more preferably about 325° F. to about 360° F., and the stock isheld at that temperature for at least about 10 minutes to about 30minutes.

The thermoset rubber composition of the present invention may alsoinclude an optional soft and fast agent. As used herein, “soft and fastagent” means any compound or a blend thereof that that is capable ofmaking a core 1) be softer (lower compression) at constant COR or 2)have a higher COR at equal compression, or any combination thereof, whencompared to a core equivalently prepared without a soft and fast agent.Preferably, the composition of the present invention contains from about0.05 phr to about 10.0 phr soft and fast agent. In one embodiment, thesoft and fast agent is present in an amount of about 0.05 phr to about3.0 phr, preferably about 0.05 phr to about 2.0 phr, more preferablyabout 0.05 phr to about 1.0 phr. In another embodiment, the soft andfast agent is present in an amount of about 2.0 phr to about 5.0 phr,preferably about 2.35 phr to about 4.0 phr, and more preferably about2.35 phr to about 3.0 phr. In an alternative high concentrationembodiment, the soft and fast agent is present in an amount of about 5.0phr to about 10.0 phr, more preferably about 6.0 phr to about 9.0 phr,most preferably about 7.0 phr to about 8.0 phr. In a most preferredembodiment, the soft and fast agent is present in an amount of about 2.6phr.

Suitable soft and fast agents include, but are not limited to,organosulfur or metal-containing organosulfur compounds, an organicsulfur compound, including mono, di, and polysulfides, a thiol, ormercapto compound, an inorganic sulfide compound, a Group VIA compound,or mixtures thereof. The soft and fast agent component may also be ablend of an organosulfur compound and an inorganic sulfide compound.

Suitable soft and fast agents of the present invention include, but arenot limited to those having the following general formula:

where R₁-R₅ can be C₁-C₈ alkyl groups; halogen groups; thiol groups(—SH), carboxylated groups; sulfonated groups; and hydrogen; in anyorder; and also pentafluorothiophenol; 2-fluorothiophenol;3-fluorothiophenol; 4-fluorothiophenol; 2,3-fluorothiophenol;2,4-fluorothiophenol; 3,4-fluorothiophenol; 3,5-fluorothiophenol2,3,4-fluorothiophenol; 3,4,5-fluorothiophenol;2,3,4,5-tetrafluorothiophenol; 2,3,5,6-tetrafluorothiophenol;4-chlorotetrafluorothiophenol; pentachlorothiophenol;2-chlorothiophenol; 3-chlorothiophenol; 4-chlorothiophenol;2,3-chlorothiophenol; 2,4-chlorothiophenol; 3,4-chlorothiophenol;3,5-chlorothiophenol; 2,3,4-chlorothiophenol; 3,4,5-chlorothiophenol;2,3,4,5-tetrachlorothiophenol; 2,3,5,6-tetrachlorothiophenol;pentabromothiophenol; 2-bromothiophenol; 3-bromothiophenol;4-bromothiophenol; 2,3-bromothiophenol; 2,4-bromothiophenol;3,4-bromothiophenol; 3,5-bromothiophenol; 2,3,4-bromothiophenol;3,4,5-bromothiophenol; 2,3,4,5-tetrabromothiophenol;2,3,5,6-tetrabromothiophenol; pentaiodothiophenol; 2-iodothiophenol;3-iodothiophenol; 4-iodothiophenol; 2,3-iodothiophenol;2,4-iodothiophenol; 3,4-iodothiophenol; 3,5-iodothiophenol;2,3,4-iodothiophenol; 3,4,5-iodothiophenol; 2,3,4,5-tetraiodothiophenol;2,3,5,6-tetraiodothiophenoland; and their zinc salts. Preferably, thehalogenated thiophenol compound is pentachlorothiophenol, which iscommercially available in neat form or under the tradename STRUKTOL®, aclay-based carrier containing the sulfur compound pentachlorothiophenolloaded at 45 percent. STRUKTOL® is commercially available from StruktolCompany of America of Stow, Ohio. PCTP is commercially available in neatform from eChinachem of San Francisco, Calif. and in the salt form fromeChinachem of San Francisco, Calif. Most preferably, the halogenatedthiophenol compound is the zinc salt of pentachlorothiophenol, which iscommercially available from eChinachem of San Francisco, Calif.

Other suitable soft and fast agents include, but are not limited to,hydroquinones, benzoquinones, quinhydrones, catechols, and resorcinols.

Suitable hydroquinone compounds include compounds represented by thefollowing formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are hydrogen; halogen; alkyl; carboxyl;metal salts thereof, and esters thereof, acetate and esters thereof;formyl; acyl; acetyl; halogenated carbonyl; sulfo and esters thereof;halogenated sulfonyl; sulfino; alkylsulfinyl; carbamoyl; halogenatedalkyl; cyano; alkoxy; hydroxy and metal salts thereof; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Other suitable hydroquinone compounds include, but are not limited to,hydroquionone; tetrachlorohydroquinone; 2-chlorohydroquionone;2-bromohydroquinone; 2,5-dichlorohydroquinone; 2,5-dibromohydroquinone;tetrabromohydroquinone; 2-methylhydroquinone; 2-t-butylhydroquinone;2,5-di-t-amylhydroquinone; and 2-(2-chlorophenyl)hydroquinone hydrate.

More suitable hydroquinone compounds include compounds represented bythe following formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are a metal salt of a carboxyl; acetateand esters thereof; hydroxy; a metal salt of a hydroxy; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Suitable benzoquinone compounds include compounds represented by thefollowing formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are hydrogen; halogen; alkyl; carboxyl;metal salts thereof, and esters thereof; acetate and esters thereof;formyl; acyl; acetyl; halogenated carbonyl; sulfo and esters thereof;halogenated sulfonyl; sulfino; alkylsulfinyl; carbamoyl; halogenatedalkyl; cyano; alkoxy; hydroxy and metal salts thereof; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Other suitable benzoquinone compounds include one or more compoundsrepresented by the following formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are a metal salt of a carboxyl; acetateand esters thereof; hydroxy; a metal salt of a hydroxy; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Suitable quinhydrones include one or more compounds represented by thefollowing formula, and hydrates thereof:

wherein each R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ are hydrogen; halogen;alkyl; carboxyl; metal salts thereof, and esters thereof; acetate andesters thereof; formyl; acyl; acetyl; halogenated carbonyl; sulfo andesters thereof; halogenated sulfonyl; sulfino; alkylsulfinyl; carbamoyl;halogenated alkyl; cyano; alkoxy; hydroxy and metal salts thereof;amino; nitro; aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Other suitable quinhydrones include those having the above formula,wherein each R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ are a metal salt of acarboxyl; acetate and esters thereof; hydroxy; a metal salt of ahydroxy; amino; nitro; aryl; aryloxy; arylalkyl; nitroso; acetamido; orvinyl. Suitable catechols include one or more compounds represented bythe following formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are hydrogen; halogen; alkyl; carboxyl;metal salts thereof, and esters thereof; acetate and esters thereof;formyl; acyl; acetyl; halogenated carbonyl; sulfo and esters thereof;halogenated sulfonyl; sulfino; alkylsulfinyl; carbamoyl; halogenatedalkyl; cyano; alkoxy; hydroxy and metal salts thereof; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Suitable resorcinols include one or more compounds represented by thefollowing formula, and hydrates thereof:

wherein each R₁, R₂, R₃, and R₄ are hydrogen; halogen; alkyl; carboxyl;metal salts thereof, and esters thereof; acetate and esters thereof;formyl; acyl; acetyl; halogenated carbonyl; sulfo and esters thereof;halogenated sulfonyl; sulfino; alkylsulfinyl; carbamoyl; halogenatedalkyl; cyano; alkoxy; hydroxy and metal salts thereof; amino; nitro;aryl; aryloxy; arylalkyl; nitroso; acetamido; or vinyl.

Fillers may also be added to the thermoset rubber composition of thecore to adjust the density of the composition, up or down. Typically,fillers include materials such as tungsten, zinc oxide, barium sulfate,silica, calcium carbonate, zinc carbonate, metals, metal oxides andsalts, regrind (recycled core material typically ground to about 30 meshparticle), high-Mooney-viscosity rubber regrind, trans-regrind corematerial (recycled core material containing high trans-isomer ofpolybutadiene), and the like. When trans-regrind is present, the amountof trans-isomer is preferably between about 10% and about 60%. In apreferred embodiment of the invention, the core comprises polybutadienehaving a cis-isomer content of greater than about 95% and trans-regrindcore material (already vulcanized) as a filler. Any particle sizetrans-regrind core material is sufficient, but is preferably less thanabout 125 μm.

Fillers added to one or more portions of the golf ball typically includeprocessing aids or compounds to affect rheological and mixingproperties, density-modifying fillers, tear strength, or reinforcementfillers, and the like. The fillers are generally inorganic, and suitablefillers include numerous metals or metal oxides, such as zinc oxide andtin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate,barium carbonate, clay, tungsten, tungsten carbide, an array of silicas,and mixtures thereof. Fillers may also include various foaming agents orblowing agents which may be readily selected by one of ordinary skill inthe art. Fillers may include polymeric, ceramic, metal, and glassmicrospheres may be solid or hollow, and filled or unfilled. Fillers aretypically also added to one or more portions of the golf ball to modifythe density thereof to conform to uniform golf ball standards. Fillersmay also be used to modify the weight of the center or at least oneadditional layer for specialty balls, e.g., a lower weight ball ispreferred for a player having a low swing speed.

Materials such as tungsten, zinc oxide, barium sulfate, silica, calciumcarbonate, zinc carbonate, metals, metal oxides and salts, and regrind(recycled core material typically ground to about 30 mesh particle) arealso suitable fillers.

The polybutadiene and/or any other base rubber or elastomer system mayalso be foamed, or filled with hollow microspheres or with expandablemicrospheres which expand at a set temperature during the curing processto any low specific gravity level. Other ingredients such as sulfuraccelerators, e.g., tetra methylthiuram di, tri, or tetrasulfide, and/ormetal-containing organosulfur components may also be used according tothe invention. Suitable metal-containing organosulfur acceleratorsinclude, but are not limited to, cadmium, copper, lead, and telluriumanalogs of diethyldithiocarbamate, diamyldithiocarbamate, anddimethyldithiocarbamate, or mixtures thereof. Other ingredients such asprocessing aids e.g., fatty acids and/or their metal salts, processingoils, dyes and pigments, as well as other additives known to one skilledin the art may also be used in the present invention in amountssufficient to achieve the purpose for which they are typically used.

A number of cores were formed based on the formulation and cure cycledescribed in TABLE 1 below and core hardness values are reported inTABLE 2 below.

TABLE 1 Formulation (phr) Ex 1 Ex 2 Ex 3 Comp Ex 1 Comp Ex 2 Comp Ex 3SR-526⁺ 34.0 34.0 31.2 29.0 29.0 29.0 ZnO 5 5 5 5 5 5 BaSO₄ 11.2 11.216.1 13.8 13.8 13.8 Vanox MBPC* 0.40 0.40 0.40 — 0.50 —Trigonox-265-50B** 1.4 1.4 1.6 — — 0.8 Perkadox BC-FF*** — — — 1.0 1.6 —polybutadiene 100 100 100 100 100 100 ZnPCTP 2.35 2.35 2.60 2.35 2.352.35 regrind — — 17 17 — — antioxidant/initiator ratio 0.57 0.57 0.50 —0.31 — Cure Temp. (° F.) 305 315 320 350 335 335 Cure Time (min) 14 1116 11 11 11 Properties diameter (in) 1.530 1.530 1.530 1.530 1.530 1.530compression 69 63 70 69 47 — COR @ 125 ft/s 0.808 0.806 0.804 0.804 — —*Vanox MBPC: 2,2′-methylene-bis-(4-methyl-6-t-butylphenol) availablefrom R. T. Vanderbilt Company Inc.; **Trigonox 265-50B: a mixture of1,1-di(t-butylperoxy)-3,3,5-trimethycyclohexane anddi(2-t-butylperoxyisopropyl)benzene 50% active on an inert carrieravailable from Akzo Nobel; ***Perkadox BC-FF: Dicumyl peroxide (99%-100%active) available from Akzo Nobel; and ⁺SR-526: ZDA available fromSartomer

TABLE 2 Shore C Hardness Distance from Comp Comp Comp Center Ex 1 Ex 2Ex 3 Ex 1 Ex 2 Ex 3 Center 73 70 71 61 52 61 2 74 71 72 67 57 62 4 74 7273 70 62 65 6 75 73 73 72 64 67 8 75 73 73 73 64 69 10 75 73 74 73 64 7112 74 74 73 72 66 72 14 74 74 72 73 70 73 16 70 71 70 77 71 73 18 60 6063 80 72 73 Surface 63 70 66 85 73 74 Surface − Center −10 0 −5 24 21 13

The surface hardness of a core is obtained from the average of a numberof measurements taken from opposing hemispheres of a core, taking careto avoid making measurements on the parting line of the core or onsurface defects, such as holes or protrusions. Hardness measurements aremade pursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plasticby Means of a Durometer.” Because of the curved surface of a core, caremust be taken to insure that the core is centered under the durometerindentor before a surface hardness reading is obtained. A calibrated,digital durometer, capable of reading to 0.1 hardness units is used forall hardness measurements and is set to take hardness readings at 1second after the maximum reading is obtained. The digital durometer mustbe attached to, and its foot made parallel to, the base of an automaticstand, such that the weight on the durometer and attack rate conform toASTM D-2240.

To prepare a core for hardness gradient measurements, the core is gentlypressed into a hemispherical holder having an internal diameterapproximately slightly smaller than the diameter of the core, such thatthe core is held in place in the hemispherical portion of the holderwhile concurrently leaving the geometric central plane of the coreexposed. The core is secured in the holder by friction, such that itwill not move during the cutting and grinding steps, but the friction isnot so excessive that distortion of the natural shape of the core wouldresult. The core is secured such that the parting line of the core isroughly parallel to the top of the holder. The diameter of the core ismeasured 90 degrees to this orientation prior to securing. A measurementis also made from the bottom of the holder to the top of the core toprovide a reference point for future calculations. A rough cut, madeslightly above the exposed geometric center of the core using a band sawor other appropriate cutting tool, making sure that the core does notmove in the holder during this step. The remainder of the core, still inthe holder, is secured to the base plate of a surface grinding machine.The exposed ‘rough’ core surface is ground to a smooth, flat surface,revealing the geometric center of the core, which can be verified bymeasuring the height of the bottom of the holder to the exposed surfaceof the core, making sure that exactly half of the original height of thecore, as measured above, has been removed to within ±0.004 inches.

Leaving the core in the holder, the center of the core is found with acenter square and carefully marked and the hardness is measured at thecenter mark. Hardness measurements at any distance from the center ofthe core may be measured by drawing a line radially outward from thecenter mark, and measuring and marking the distance from the center,typically in 2-mm increments. All hardness measurements performed on theplane passing through the geometric center are performed while the coreis still in the holder and without having disturbed its orientation,such that the test surface is constantly parallel to the bottom of theholder. The hardness difference from any predetermined location on thecore is calculated as the average surface hardness minus the hardness atthe appropriate reference point, e.g., at the center of the core forsingle, solid core, such that a core surface softer than its center willhave a negative hardness gradient.

Referring to TABLES 1-2, in Example 1, the surface is 10 Shore C pointslower than the center hardness and 12 Shore C points lower than thehardest point in the core. In Example 3, the surface is 5 Shore C pointslower than the center hardness and 8 Shore C points lower than thehardest point in the core. In Example 2, the center and surface hardnessvalues are equal and the softest point in the core is 10 Shore C pointslower than the surface.

In the examples of the invention presented in TABLE 1, the curetemperatures are varied from 305° F. to 320° F. and cure times arevaried from 11 to 16 minutes. The core compositions of examples 1 and 2are identical, and only the cure cycle is changed. In example 3 theamount of antioxidant is identical to examples 1 and 2, but otheringredients are varied as well the cure cycle. Additionally, the ratioof antioxidant to initiator varies from 0.50 to 0.57 from example 1 and2 to example 3.

The ratio of antioxidant to initiator is one factor to control thesurface hardness of the cores. The data shown in TABLE 2 shows thathardness gradient is at least, but not limited to, a function of theamount of antioxidant and peroxide, their ratio, and the cure cycle. Itshould be noted that higher antioxidant also requires higher peroxideinitiator to maintain the desired compression.

In FIG. 1, cores of Comparative Examples 1-3 are compared to theinventive cores. The core of Comparative Example 1, whose composition isshown in TABLE 1 was cured using a conventional cure cycle, with a curetemperature of 350° F. and a cure time of 11 minutes. The inventivecores were produced using cure cycles of 305° F. for 14 minutes, 315° F.for 11 minutes and 320° F. for 16 minutes. The hardness gradients ofthese cores were measured and the following observations can be made.For the cores of the Comparative Examples, as expected, a conventionalhard surface to soft center gradient can be clearly seen. The gradientsfor inventive cores follow substantially the same shape as one another.

In some embodiments of invention, the hardness of the core at thesurface is at most about the same as or substantially less than thehardness of the core at the center. Furthermore, the center hardness ofthe core may not be the hardest point in the core, but in all cases, itis preferred that it is at least equal to or harder than the surface.Additionally, the lowest hardness anywhere in the core does not have tooccur at the surface. In some embodiments, the lowest hardness valueoccurs within about the outer 6 mm of the core surface. However, thelowest hardness value within the core can occur at any point from thesurface, up to, but not including the center, as long as the surfacehardness is still equal to, or less than the hardness of the center. Itshould be noted that in the present invention the formulation is thesame throughout the core, or core layer, and no surface treatment isapplied to the core to obtain the preferred surface hardness.

While the inventive golf ball may be formed from a variety of differingand conventional cover materials (both intermediate layer(s) and outercover layer), preferred cover materials include, but are not limited to:

-   -   (1) Polyurethanes, such as those prepared from polyols or        polyamines and diisocyanates or polyisocyanates and/or their        prepolymers, and those disclosed in U.S. Pat. Nos. 5,334,673 and        6,506,851;    -   (2) Polyureas, such as those disclosed in U.S. Pat. Nos.        5,484,870 and 6,835,794; and    -   (3) Polyurethane-urea hybrids, blends or copolymers comprising        urethane or urea segments.

Suitable polyurethane compositions comprise a reaction product of atleast one polyisocyanate and at least one curing agent. The curing agentcan include, for example, one or more polyamines, one or more polyols,or a combination thereof. The polyisocyanate can be combined with one ormore polyols to form a prepolymer, which is then combined with the atleast one curing agent. Thus, the polyols described herein are suitablefor use in one or both components of the polyurethane material, i.e., aspart of a prepolymer and in the curing agent. Suitable polyurethanes aredescribed in U.S. Patent Application Publication No. 2005/0176523, whichis incorporated by reference in its entirety.

Any polyisocyanate available to one of ordinary skill in the art issuitable for use according to the invention. Exemplary polyisocyanatesinclude, but are not limited to, 4,4′-diphenylmethane diisocyanate(MDI); polymeric MDI; carbodiimide-modified liquid MDI;4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI); p-phenylene diisocyanate(PPDI); m-phenylene diisocyanate (MPDI); toluene diisocyanate (TDI);3,3′-dimethyl-4,4′-biphenylene diisocyanate; isophoronediisocyanate;1,6-hexamethylene diisocyanate (HDI); naphthalene diisocyanate; xylenediisocyanate; p-tetramethylxylene diisocyanate; m-tetramethylxylenediisocyanate; ethylene diisocyanate; propylene-1,2-diisocyanate;tetramethylene-1,4-diisocyanate; cyclohexyl diisocyanate;dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; methylcyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of2,4,4-trimethyl-1,6-hexane diisocyanate; tetracene diisocyanate;napthalene diisocyanate; anthracene diisocyanate; isocyanurate oftoluene diisocyanate; uretdione of hexamethylene diisocyanate; andmixtures thereof. Polyisocyanates are known to those of ordinary skillin the art as having more than one isocyanate group, e.g.,di-isocyanate, tri-isocyanate, and tetra-isocyanate. Preferably, thepolyisocyanate includes MDI, PPDI, TDI, or a mixture thereof, and morepreferably, the polyisocyanate includes MDI. It should be understoodthat, as used herein, the term MDI includes 4,4′-diphenylmethanediisocyanate, polymeric MDI, carbodiimide-modified liquid MDI, andmixtures thereof and, additionally, that the diisocyanate employed maybe “low free monomer,” understood by one of ordinary skill in the art tohave lower levels of “free” monomer isocyanate groups, typically lessthan about 0.1% free monomer isocyanate groups. Examples of “low freemonomer” diisocyanates include, but are not limited to Low Free MonomerMDI, Low Free Monomer TDI, and Low Free Monomer PPDI.

The at least one polyisocyanate should have less than about 14%unreacted NCO groups. Preferably, the at least one polyisocyanate has nogreater than about 8.0% NCO, more preferably no greater than about 7.8%,and most preferably no greater than about 7.5% NCO with a level of NCOof about 7.2 or 7.0, or 6.5% NCO commonly used.

Any polyol available to one of ordinary skill in the art is suitable foruse according to the invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

In another embodiment, polyester polyols are included in thepolyurethane material. Suitable polyester polyols include, but are notlimited to, polyethylene adipate glycol; polybutylene adipate glycol;polyethylene propylene adipate glycol; o-phthalate-1,6-hexanediol;poly(hexamethylene adipate) glycol; and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups.

In another embodiment, polycaprolactone polyols are included in thematerials of the invention. Suitable polycaprolactone polyols include,but are not limited to, 1,6-hexanediol-initiated polycaprolactone,diethylene glycol initiated polycaprolactone, trimethylol propaneinitiated polycaprolactone, neopentyl glycol initiated polycaprolactone,1,4-butanediol-initiated polycaprolactone, and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups.

In yet another embodiment, polycarbonate polyols are included in thepolyurethane material of the invention. Suitable polycarbonates include,but are not limited to, polyphthalate carbonate and poly(hexamethylenecarbonate) glycol. The hydrocarbon chain can have saturated orunsaturated bonds, or substituted or unsubstituted aromatic and cyclicgroups. In one embodiment, the molecular weight of the polyol is fromabout 200 to about 4000. Polyamine curatives are also suitable for usein the polyurethane composition of the invention and have been found toimprove cut, shear, and impact resistance of the resultant balls.Preferred polyamine curatives include, but are not limited to,3,5-dimethylthio-2,4-toluenediamine and isomers thereof;3,5-diethyltoluene-2,4-diamine and isomers thereof, such as3,5-diethyltoluene-2,6-diamine;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline);polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyldiamino diphenylmethane; p,p′-methylene dianiline; m-phenylenediamine;4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-methylene-bis-(2,3-dichloroaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane; trimethylene glycoldi-p-aminobenzoate; and mixtures thereof. Preferably, the curing agentof the present invention includes 3,5-dimethylthio-2,4-toluenediamineand isomers thereof, such as ETHACURE® 300, commercially available fromAlbermarle Corporation of Baton Rouge, La. Suitable polyamine curatives,which include both primary and secondary amines, preferably havemolecular weights ranging from about 64 to about 2000.

At least one of a diol, triol, tetraol, or hydroxy-terminated curativesmay be added to the aforementioned polyurethane composition. Suitablediol, triol, and tetraol groups include ethylene glycol; diethyleneglycol; polyethylene glycol; propylene glycol; polypropylene glycol;lower molecular weight polytetramethylene ether glycol;1,3-bis(2-hydroxyethoxy) benzene; 1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene; 1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene;1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol;resorcinol-di-(β-hydroxyethyl)ether;hydroquinone-di-(β-hydroxyethyl)ether; and mixtures thereof. Preferredhydroxy-terminated curatives include 1,3-bis(2-hydroxyethoxy) benzene;1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene; 1,4-butanediol,and mixtures thereof. Preferably, the hydroxy-terminated curatives havemolecular weights ranging from about 48 to 2000. It should be understoodthat molecular weight, as used herein, is the absolute weight averagemolecular weight and would be understood as such by one of ordinaryskill in the art.

Both the hydroxy-terminated and amine curatives can include one or moresaturated, unsaturated, aromatic, and cyclic groups. Additionally, thehydroxy-terminated and amine curatives can include one or more halogengroups. The polyurethane composition can be formed with a blend ormixture of curing agents. If desired, however, the polyurethanecomposition may be formed with a single curing agent.

In a preferred embodiment of the present invention, saturatedpolyurethanes are used to form one or more of the cover layers,preferably the outer cover layer, and may be selected from among bothcastable thermoset and thermoplastic polyurethanes.

In this embodiment, the saturated polyurethanes of the present inventionare substantially free of aromatic groups or moieties. Saturatedpolyurethanes suitable for use in the invention are a product of areaction between at least one polyurethane prepolymer and at least onesaturated curing agent. The polyurethane prepolymer is a product formedby a reaction between at least one saturated polyol and at least onesaturated diisocyanate. As is well known in the art, that a catalyst maybe employed to promote the reaction between the curing agent and theisocyanate and polyol, or the curing agent and the prepolymer.

Saturated diisocyanates which can be used include, without limitation,ethylene diisocyanate; propylene-1,2-diisocyanate;tetramethylene-1,4-diisocyanate; 1,6-hexamethylene-diisocyanate (HDI);2,2,4-trimethylhexamethylene diisocyanate; 2,4,4-trimethylhexamethylenediisocyanate; dodecane-1,12-diisocyanate; dicyclohexylmethanediisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; isophoronediisocyanate; methyl cyclohexylene diusocyanate; triisocyanate of HDI;triisocyanate of 2,2,4-trimethyl-1,6-hexane diusocyanate. The mostpreferred saturated diisocyanates are 4,4′-dicyclohexylmethanediisocyanate and isophorone diisocyanate.

Saturated polyols which are appropriate for use in this inventioninclude without limitation polyether polyols such as polytetramethyleneether glycol and poly(oxypropylene) glycol. Suitable saturated polyesterpolyols include polyethylene adipate glycol, polyethylene propyleneadipate glycol, polybutylene adipate glycol, polycarbonate polyol andethylene oxide-capped polyoxypropylene diols. Saturated polycaprolactonepolyols which are useful in the invention include diethyleneglycol-initiated polycaprolactone, 1,4-butanediol-initiatedpolycaprolactone, 1,6-hexanediol-initiated polycaprolactone; trimethylolpropane-initiated polycaprolactone, neopentyl glycol initiatedpolycaprolactone, and polytetramethylene ether glycol-initiatedpolycaprolactone. The most preferred saturated polyols arepolytetramethylene ether glycol and PTMEG-initiated polycaprolactone.

Suitable saturated curatives include 1,4-butanediol, ethylene glycol,diethylene glycol, polytetramethylene ether glycol, propylene glycol;trimethanolpropane; tetra-(2-hydroxypropyl)-ethylenediamine; isomers andmixtures of isomers of cyclohexyldimethylol, isomers and mixtures ofisomers of cyclohexane bis(methylamine); triisopropanolamine; ethylenediamine; diethylene triamine; triethylene tetramine; tetraethylenepentamine; 4,4′-dicyclohexylmethane diamine;2,2,4-trimethyl-1,6-hexanediamine; 2,4,4-trimethyl-1,6-hexanediamine;diethyleneglycol di-(aminopropyl)ether;4,4′-bis-(sec-butylamino)-dicyclohexylmethane;1,2-bis-(sec-butylamino)cyclohexane; 1,4-bis-(sec-butylamino)cyclohexane; isophorone diamine; hexamethylene diamine; propylenediamine; 1-methyl-2,4-cyclohexyl diamine; 1-methyl-2,6-cyclohexyldiamine; 1,3-diaminopropane; dimethylamino propylamine; diethylaminopropylamine; imido-bis-propylamine; isomers and mixtures of isomers ofdiaminocyclohexane; monoethanolamine; diethanolamine; triethanolamine;monoisopropanolamine; and diisopropanolamine. The most preferredsaturated curatives are 1,4-butanediol, 1,4-cyclohexyldimethylol and4,4′-bis-(sec-butylamino)-dicyclohexylmethane. Alternatively, othersuitable polymers include partially or fully neutralized ionomer,metallocene, or other single-site catalyzed polymer, polyester,polyamide, non-ionomeric thermoplastic elastomer, copolyether-esters,copolyether-amides, polycarbonate, polybutadiene, polyisoprene,polystryrene block copolymers (such as styrene-butadiene-styrene),styrene-ethylene-propylene-styrene, styrene-ethylene-butylene-styrene,and the like, and blends thereof.

Thermosetting polyurethanes or polyureas are suitable for the outercover layers of the golf balls of the present invention.

Additionally, polyurethane can be replaced with or blended with apolyurea material. Polyureas are distinctly different from polyurethanecompositions, but also result in desirable aerodynamic and aestheticcharacteristics when used in golf ball components. The polyurea-basedcompositions are preferably saturated in nature.

Without being bound to any particular theory, it is now believed thatsubstitution of the long chain polyol segment in the polyurethaneprepolymer with a long chain polyamine oligomer soft segment to form apolyurea prepolymer, improves shear, cut, and resiliency, as well asadhesion to other components. Thus, the polyurea compositions of thisinvention may be formed from the reaction product of an isocyanate andpolyamine prepolymer crosslinked with a curing agent. For example,polyurea-based compositions of the invention may be prepared from atleast one isocyanate, at least one polyether amine, and at least onediol curing agent or at least one diamine curing agent.

Any polyamine available to one of ordinary skill in the art is suitablefor use in the polyurea prepolymer. Polyether amines are particularlysuitable for use in the prepolymer. As used herein, “polyether amines”refer to at least polyoxyalkyleneamines containing primary amino groupsattached to the terminus of a polyether backbone. Due to the rapidreaction of isocyanate and amine, and the insolubility of many ureaproducts, however, the selection of diamines and polyether amines islimited to those allowing the successful formation of the polyureaprepolymers. In one embodiment, the polyether backbone is based ontetramethylene, propylene, ethylene, trimethylolpropane, glycerin, andmixtures thereof. Suitable polyether amines include, but are not limitedto, methyldiethanolamine; polyoxyalkylenediamines such as,polytetramethylene ether diamines, polyoxypropylenetriamine, andpolyoxypropylene diamines; poly(ethylene oxide capped oxypropylene)ether diamines; propylene oxide-based triamines;triethyleneglycoldiamines; trimethylolpropane-based triamines;glycerin-based triamines; and mixtures thereof. In one embodiment, thepolyether amine used to form the prepolymer is JEFFAMINE® D2000(manufactured by Huntsman Chemical Co. of Austin, Tex.).

The molecular weight of the polyether amine for use in the polyureaprepolymer may range from about 100 to about 5000. In one embodiment,the polyether amine molecular weight is about 200 or greater, preferablyabout 230 or greater. In another embodiment, the molecular weight of thepolyether amine is about 4000 or less. In yet another embodiment, themolecular weight of the polyether amine is about 600 or greater. Instill another embodiment, the molecular weight of the polyether amine isabout 3000 or less. In yet another embodiment, the molecular weight ofthe polyether amine is between about 1000 and about 3000, and morepreferably is between about 1500 to about 2500. Because lower molecularweight polyether amines may be prone to forming solid polyureas, ahigher molecular weight oligomer, such as JEFFAMINE® D2000, ispreferred.

As briefly discussed above, some amines may be unsuitable for reactionwith the isocyanate because of the rapid reaction between the twocomponents. In particular, shorter chain amines are fast reacting. Inone embodiment, however, a hindered secondary diamine may be suitablefor use in the prepolymer. Without being bound to any particular theory,it is believed that an amine with a high level of stearic hindrance,e.g., a tertiary butyl group on the nitrogen atom, has a slower reactionrate than an amine with no hindrance or a low level of hindrance. Forexample, 4,4′-bis-(sec-butylamino)-dicyclohexylmethane (CLEARLINK® 1000)may be suitable for use in combination with an isocyanate to form thepolyurea prepolymer.

Any isocyanate available to one of ordinary skill in the art is suitablefor use in the polyurea prepolymer. Isocyanates for use with the presentinvention include aliphatic, cycloaliphatic, araliphatic, aromatic, anyderivatives thereof, and combinations of these compounds having two ormore isocyanate (NCO) groups per molecule. The isocyanates may beorganic polyisocyanate-terminated prepolymers. The isocyanate-containingreactable component may also include any isocyanate-functional monomer,dimer, trimer, or multimeric adduct thereof, prepolymer,quasi-prepolymer, or mixtures thereof. Isocyanate-functional compoundsmay include monoisocyanates or polyisocyanates that include anyisocyanate functionality of two or more.

Suitable isocyanate-containing components include diisocyanates havingthe generic structure: O═C═N—R—N═C═O, where R is preferably a cyclic,aromatic, or linear or branched hydrocarbon moiety containing from about1 to about 20 carbon atoms. The diisocyanate may also contain one ormore cyclic groups or one or more phenyl groups. When multiple cyclic oraromatic groups are present, linear and/or branched hydrocarbonscontaining from about 1 to about 10 carbon atoms can be present asspacers between the cyclic or aromatic groups. In some cases, the cyclicor aromatic group(s) may be substituted at the 2-, 3-, and/or4-positions, or at the ortho-, meta-, and/or para-positions,respectively. Substituted groups may include, but are not limited to,halogens, primary, secondary, or tertiary hydrocarbon groups, or amixture thereof.

Examples of diisocyanates that can be used with the present inventioninclude, but are not limited to, substituted and isomeric mixturesincluding 2,2′-, 2,4′-, and 4,4′-diphenylmethane diisocyanate;3,3′-dimethyl-4,4′-biphenylene diisocyanate; toluene diisocyanate;polymeric MDI; carbodiimide-modified liquid 4,4′-diphenylmethanediisocyanate; para-phenylene diisocyanate; meta-phenylene diisocyanate;triphenyl methane-4,4′- and triphenyl methane-4,4′-triisocyanate;naphthylene-1,5-diisocyanate; 2,4′-, 4,4′-, and 2,2-biphenyldiisocyanate; polyphenyl polymethylene polyisocyanate; mixtures of MDIand PMDI; mixtures of PMDI and TDI; ethylene diisocyanate;propylene-1,2-diisocyanate; tetramethylene-1,2-diisocyanate;tetramethylene-1,3-diisocyanate; tetramethylene-1,4-diisocyanate;1,6-hexamethylene-diisocyanate; octamethylene diisocyanate;decamethylene diisocyanate; 2,2,4-trimethylhexamethylene diisocyanate;2,4,4-trimethylhexamethylene diisocyanate; dodecane-1,12-diisocyanate;cyclobutane-1,3-diisocyanate; cyclohexane-1,2-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;methyl-cyclohexylene diisocyanate; 2,4-methylcyclohexane diisocyanate;2,6-methylcyclohexane diisocyanate; 4,4′-dicyclohexyl diisocyanate;2,4′-dicyclohexyl diisocyanate; 1,3,5-cyclohexane triisocyanate;isocyanatomethylcyclohexane isocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane;isocyanatoethylcyclohexane isocyanate; bis(isocyanatomethyl)-cyclohexanediisocyanate; 4,4′-bis(isocyanatomethyl) dicyclohexane;2,4′-bis(isocyanatomethyl) dicyclohexane; isophorone diisocyanate;triisocyanate of HDI; triisocyanate of 2,2,4-trimethyl-1,6-hexanediisocyanate; 4,4′-dicyclohexylmethane diisocyanate;2,4-hexahydrotoluene diisocyanate; 2,6-hexahydrotoluene diisocyanate;1,2-, 1,3-, and 1,4-phenylene diisocyanate; aromatic aliphaticisocyanate, such as 1,2-, 1,3-, and 1,4-xylene diisocyanate;meta-tetramethylxylene diisocyanate; para-tetramethylxylenediisocyanate; trimerized isocyanurate of any polyisocyanate, such asisocyanurate of toluene diisocyanate, trimer of diphenylmethanediisocyanate, trimer of tetramethylxylene diisocyanate, isocyanurate ofhexamethylene diisocyanate, isocyanurate of isophorone diisocyanate, andmixtures thereof; dimerized uredione of any polyisocyanate, such asuretdione of toluene diisocyanate, uretdione of hexamethylenediisocyanate, and mixtures thereof; modified polyisocyanate derived fromthe above isocyanates and polyisocyanates; and mixtures thereof.

Examples of saturated diisocyanates that can be used with the presentinvention include, but are not limited to, ethylene diisocyanate;propylene-1,2-diisocyanate; tetramethylene diisocyanate;tetramethylene-1,4-diisocyanate; 1,6-hexamethylene-diisocyanate;octamethylene diisocyanate; decamethylene diisocyanate;2,2,4-trimethylhexamethylene diisocyanate; 2,4,4-trimethylhexamethylenediisocyanate; dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,2-diisocyanate; cyclohexane-1,3-diisocyanate;cyclohexane-1,4-diisocyanate; methyl-cyclohexylene diisocyanate;2,4-methylcyclohexane diisocyanate; 2,6-methylcyclohexane diisocyanate;4,4′-dicyclohexyl diisocyanate; 2,4′-dicyclohexyl diisocyanate;1,3,5-cyclohexane triisocyanate; isocyanatomethylcyclolhexaneisocyanate; 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane;isocyanatoethylcyclohexane isocyanate; bis(isocyanatomethyl)-cyclohexanediisocyanate; 4,4′-bis(isocyanatomethyl) dicyclohexane;2,4′-bis(isocyanatomethyl) dicyclohexane; isophorone diisocyanate;triisocyanate of HDI; triisocyanate of 2,2,4-trimethyl-1,6-hexanediisocyanate; 4,4′-dicyclohexylmethane diisocyanate;2,4-hexahydrotoluene diisocyanate; 2,6-hexahydrotoluene diisocyanate;and mixtures thereof. Aromatic aliphatic isocyanates may also be used toform light stable materials. Examples of such isocyanates include 1,2-,1,3-, and 1,4-xylene diisocyanate; meta-tetramethylxylene diisocyanate;para-tetramethylxylene diisocyanate; trimerized isocyanurate of anypolyisocyanate, such as isocyanurate of toluene diisocyanate, trimer ofdiphenylmethane diisocyanate, trimer of tetramethylxylene diisocyanate,isocyanurate of hexamethylene diisocyanate, isocyanurate of isophoronediisocyanate, and mixtures thereof; dimerized uredione of anypolyisocyanate, such as uretdione of toluene diisocyanate, uretdione ofhexamethylene diisocyanate, and mixtures thereof; modifiedpolyisocyanate derived from the above isocyanates and polyisocyanates;and mixtures thereof. In addition, the aromatic aliphatic isocyanatesmay be mixed with any of the saturated isocyanates listed above for thepurposes of this invention.

The number of unreacted NCO groups in the polyurea prepolymer ofisocyanate and polyether amine may be varied to control such factors asthe speed of the reaction, the resultant hardness of the composition,and the like. For instance, the number of unreacted NCO groups in thepolyurea prepolymer of isocyanate and polyether amine may be less thanabout 14 percent. In one embodiment, the polyurea prepolymer has fromabout 5 percent to about 11 percent unreacted NCO groups, and even morepreferably has from about 6 to about 9.5 percent unreacted NCO groups.In one embodiment, the percentage of unreacted NCO groups is about 3percent to about 9 percent. Alternatively, the percentage of unreactedNCO groups in the polyurea prepolymer may be about 7.5 percent or less,and more preferably, about 7 percent or less. In another embodiment, theunreacted NCO content is from about 2.5 percent to about 7.5 percent,and more preferably from about 4 percent to about 6.5 percent.

When formed, polyurea prepolymers may contain about 10 percent to about20 percent by weight of the prepolymer of free isocyanate monomer. Thus,in one embodiment, the polyurea prepolymer may be stripped of the freeisocyanate monomer. For example, after stripping, the prepolymer maycontain about 1 percent or less free isocyanate monomer. In anotherembodiment, the prepolymer contains about 0.5 percent by weight or lessof free isocyanate monomer.

The polyether amine may be blended with additional polyols to formulatecopolymers that are reacted with excess isocyanate to form the polyureaprepolymer. In one embodiment, less than about 30 percent polyol byweight of the copolymer is blended with the saturated polyether amine.In another embodiment, less than about 20 percent polyol by weight ofthe copolymer, preferably less than about 15 percent by weight of thecopolymer, is blended with the polyether amine. The polyols listed abovewith respect to the polyurethane prepolymer, e.g., polyether polyols,polycaprolactone polyols, polyester polyols, polycarbonate polyols,hydrocarbon polyols, other polyols, and mixtures thereof, are, alsosuitable for blending with the polyether amine. The molecular weight ofthese polymers may be from about 200 to about 4000, but also may be fromabout 1000 to about 3000, and more preferably are from about 1500 toabout 2500.

The polyurea composition can be formed by crosslinking the polyureaprepolymer with a single curing agent or a blend of curing agents. Thecuring agent of the invention is preferably an amine-terminated curingagent, more preferably a secondary diamine curing agent so that thecomposition contains only urea linkages. In one embodiment, theamine-terminated curing agent may have a molecular weight of about 64 orgreater. In another embodiment, the molecular weight of the amine-curingagent is about 2000 or less. As discussed above, certainamine-terminated curing agents may be modified with a compatibleamine-terminated freezing point depressing agent or mixture ofcompatible freezing point depressing agents.

Suitable amine-terminated curing agents include, but are not limited to,ethylene diamine; hexamethylene diamine; 1-methyl-2,6-cyclohexyldiamine; tetrahydroxypropylene ethylene diamine; 2,2,4- and2,4,4-trimethyl-1,6-hexanediamine;4,4′-bis-(sec-butylamino)-dicyclohexylmethane;1,4-bis-(sec-butylamino)-cyclohexane;1,2-bis-(sec-butylamino)-cyclohexane; derivatives of4,4′-bis-(sec-butylamino)-dicyclohexylmethane; 4,4′-dicyclohexylmethanediamine; 1,4-cyclohexane-bis-(methylamine);1,3-cyclohexane-bis-(methylamine); diethylene glycoldi-(aminopropyl)ether; 2-methylpentamethylene-diamine;diaminocyclohexane; diethylene triamine; triethylene tetramine;tetraethylene pentamine; propylene diamine; 1,3-diaminopropane;dimethylamino propylamine; diethylamino propylamine; dipropylenetriamine; imido-bis-propylamine; monoethanolamine, diethanolamine;triethanolamine; monoisopropanolamine, diisopropanolamine;isophoronediamine; 4,4-methylenebis-(2-chloroaniline); 3,5;dimethylthio-2,4-toluenediamine; 3,5-dimethylthio-2,6-toluenediamine;3,5-diethylthio-2,4-toluenediamine; 3,5; diethylthio-2,6-toluenediamine;4,4′-bis-(sec-butylamino)-diphenylmethane and derivatives thereof;1,4-bis-(sec-butylamino)-benzene; 1,2-bis-(sec-butylamino)-benzene;N,N′-dialkylamino-diphenylmethane; N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylene diamine;trimethyleneglycol-di-p-aminobenzoate;polytetramethyleneoxide-di-p-aminobenzoate;4,4′-methylenebis-(3-chloro-2,6-diethyleneaniline);4,4′-methylenebis-(2,6-diethylaniline); meta-phenylenediamine;paraphenylenediamine; and mixtures thereof. In one embodiment, theamine-terminated curing agent is4,4′-bis-(sec-butylamino)-dicyclohexylmethane.

Suitable saturated amine-terminated curing agents include, but are notlimited to, ethylene diamine; hexamethylene diamine;1-methyl-2,6-cyclohexyl diamine; tetrahydroxypropylene ethylene diamine;2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine;4,4′-bis-(sec-butylamino)-dicyclohexylmethane;1,4-bis-(sec-butylamino)-cyclohexane;1,2-bis-(sec-butylamino)-cyclohexane; derivatives of4,4′-bis-(sec-butylamino)-dicyclohexylmethane; 4,4′-dicyclohexylmethanediamine; 4,4′-methylenebis-(2,6-diethylaminocyclohexane;1,4-cyclohexane-bis-(methylamine); 1,3-cyclohexane-bis-(methylamine);diethylene glycol di-(aminopropyl)ether; 2-methylpentamethylene-diamine;diaminocyclohexane; diethylene triamine; triethylene tetramine;tetraethylene pentamine; propylene diamine; 1,3-diaminopropane;dimethylamino propylamine; diethylamino propylamine;imido-bis-propylamine; mono ethanol amine, diethanolamine;triethanolamine; monoisopropanolamine, diisopropanolamine;isophoronediamine; triisopropanolamine; and mixtures thereof. Inaddition, any of the polyether amines listed above may be used as curingagents to react with the polyurea prepolymers.

Cover layers of the inventive golf ball may also be formed fromionomeric polymers, preferably highly-neutralized ionomers (HNP). In apreferred embodiment, at least one intermediate layer of the golf ballis formed from an HNP material or a blend of HNP materials. The acidmoieties of the HNP's, typically ethylene-based ionomers, are preferablyneutralized greater than about 70%, more preferably greater than about90%, and most preferably at least about 100%. The HNP's can be also beblended with a second polymer component, which, if containing an acidgroup, may be neutralized in a conventional manner, by the organic fattyacids of the present invention, or both. The second polymer component,which may be partially or fully neutralized, preferably comprisesionomeric copolymers and telpolymers, ionomer precursors,thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes,polyureas, thermoplastic elastomers, polybutadiene rubber, balata,metallocene-catalyzed polymers (grafted and non-grafted), single-sitepolymers, high-crystalline acid polymers, cationic ionomers, and thelike. HNP polymers typically have a material hardness of between about20 and about 80 Shore D, and a flexural modulus of between about 3,000psi and about 200,000 psi.

In one embodiment of the present invention the HNP's are ionomers and/ortheir acid precursors that are preferably neutralized, either fully orpartially, with organic acid copolymers or the salts thereof. The acidcopolymers are preferably α-olefin, such as ethylene, C₃₋₈α,β-ethylenically unsaturated carboxylic acid, such as acrylic andmethacrylic acid, copolymers. They may optionally contain a softeningmonomer, such as alkyl acrylate and alkyl methacrylate, wherein thealkyl groups have from 1 to 8 carbon atoms.

The acid copolymers can be described as E/X/Y copolymers where E isethylene, X is an α,β-ethylenically unsaturated carboxylic acid, and Yis a softening comonomer. In a preferred embodiment, X is acrylic ormethacrylic acid and Y is a C₁₋₈ alkyl acrylate or methacrylate ester. Xis preferably present in an amount from about 1 to about 35 weightpercent of the polymer, more preferably from about 5 to about 30 weightpercent of the polymer, and most preferably from about 10 to about 20weight percent of the polymer. Y is preferably present in an amount fromabout 0 to about 50 weight percent of the polymer, more preferably fromabout 5 to about 25 weight percent of the polymer, and most preferablyfrom about 10 to about 20 weight percent of the polymer.

Specific acid-containing ethylene copolymers include, but are notlimited to, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylicacid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate,ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylicacid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate,ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/methacrylic acid/methyl methacrylate, andethylene/acrylic acid/n-butyl methacrylate. Preferred acid-containingethylene copolymers include, ethylene/methacrylic acid/n-butyl acrylate,ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/acrylic acid/ethyl acrylate, ethylene/methacrylicacid/ethyl acrylate, and ethylene/acrylic acid/methyl acrylatecopolymers. The most preferred acid-containing ethylene copolymers are,ethylene/(meth) acrylic acid/n-butyl, acrylate, ethylene/(meth)acrylicacid/ethyl acrylate, and ethylene/(meth) acrylic acid/methyl acrylatecopolymers.

Ionomers are typically neutralized with a metal cation, such as Li, Na,Mg, K, Ca, or Zn. It has been found that by adding sufficient organicacid or salt of organic acid, along with a suitable base, to the acidcopolymer or ionomer, however, the ionomer can be neutralized, withoutlosing processability, to a level much greater than for a metal cation.Preferably, the acid moieties are neutralized greater than about 80%,preferably from 90-100%, most preferably 100% without losingprocessability. This accomplished by melt-blending an ethyleneα,β-ethylenically unsaturated carboxylic acid copolymer, for example,with an organic acid or a salt of organic acid, and adding a sufficientamount of a cation source to increase the level of neutralization of allthe acid moieties (including those in the acid copolymer and in theorganic acid) to greater than 90%, (preferably greater than 100%).

The organic acids of the present invention are aliphatic, mono- ormulti-functional (saturated, unsaturated, or multi-unsaturated) organicacids. Salts of these organic acids may also be employed. The salts oforganic acids of the present invention include the salts of barium,lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium,strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver,aluminum, tin, or calcium, salts of fatty acids, particularly stearic,behenic, erucic, oleic, linoelic or dimerized derivatives thereof. It ispreferred that the organic acids and salts of the present invention berelatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending).

The ionomers of the invention may also be more conventional ionomers,i.e., partially-neutralized with metal cations. The acid moiety in theacid copolymer is neutralized about 1 to about 90%, preferably at leastabout 20 to about 75%, and more preferably at least about 40 to about70%, to form an ionomer, by a cation such as lithium, sodium, potassium,magnesium, calcium, barium, lead, tin, zinc, aluminum, or a mixturethereof.

In one embodiment, the inventive single-layer core is enclosed with twocover layers, where the inner cover layer has a thickness of about 0.01inches to about 0.06 inches, more preferably about 0.015 inches to about0.040 inches, and most preferably about 0.02 inches to about 0.035inches, and the inner cover layer is formed from a partially- orfully-neutralized ionomer having a Shore D hardness of greater thanabout 55, more preferably greater than about 60, and most preferablygreater than about 65. In this embodiment, the outer cover layer shouldhave a thickness of about 0.015 inches to about 0.055 inches, morepreferably about 0.02 inches to about 0.04 inches, and most preferablyabout 0.025 inches to about 0.035 inches, and has a hardness of aboutShore D 60 or less, more preferably 55 or less, and most preferablyabout 52 or less. The inner cover layer should be harder than the outercover layer. In this embodiment the outer cover layer comprises apartially- or fully-neutralized iononomer, a polyurethane, polyurea, orblend thereof. A most preferred outer cover layer is a castable orreaction injection molded polyurethane, polyurea or copolymer or hybridthereof having a Shore D hardness of about 40 to about 50. A mostpreferred inner cover layer material is a partially-neutralized ionomercomprising a zinc, sodium or lithium neutralized ionomer such as SURLYN®8940, 8945, 9910, 7930, 7940, or blend thereof having a Shore D hardnessof about 63 to about 68.

In another multi-layer cover, single core embodiment, the outer coverand inner cover layer materials and thickness are the same but, thehardness range is reversed, that is, the outer cover layer is harderthan the inner cover layer.

In an alternative embodiment, the golf ball is a one-piece golf ballhaving a dimpled surface and having a surface hardness equal to or lessthan the center hardness (i.e., a negative hardness gradient). Theone-piece ball preferably has a diameter of about 1.680 inches to about1.690 inches, a weight of about 1.620 oz, an Atti compression of fromabout 40 to 120, and a COR of about 0.750-0.825.

In a two-piece ball embodiment, the single-layer core having a negativehardness gradient is enclosed with a single layer of cover materialhaving a Shore D hardness of from about 20 to about 80, more preferablyabout 40 to about 75 and most preferably about 45 to about 70, andcomprises a thermoplastic or thermosetting polyurethane, polyurea,polyamide, polyester, polyester elastomer, polyether-amide orpolyester-amide, partially or fully neutralized ionomer, polyolefin suchas polyethylene, polypropylene, polyethylene copolymers such asethylene-butyl acrylate or ethylene-methyl acrylate, poly(ethylenemethacrylic acid) co- and terpolymers, metallocene-catalyzed polyolefinsand polar-group functionalized polyolefins and blends thereof. Apreferred cover material in the two-piece embodiment is an ionomer(either conventional or HNP) having a hardness of about 50 to about 70Shore D. Another preferred cover material in the two-piece embodiment isa thermoplastic or thermosetting polyurethane or polyurea. A preferredionomer is a high acid ionomer comprising a copolymer of ethylene andmethacrylic or acrylic acid and having an acid content of at least 16 toabout 25 weight percent. In this case the reduced spin contributed bythe relatively rigid high acid ionomer may be offset to some extent bythe spin-increasing negative gradient core. The core may have a diameterof about 1.0 inch to about 1.64 inches, preferably about 1.30 inches toabout 1.620, and more preferably about 1.40 inches to about 1.60 inches.

Another preferred cover material comprises a castable or reactioninjection moldable polyurethane, polyurea, or copolymer or hybrid ofpolyurethane/polyurea. Preferably, this cover is thermosetting but maybe a thermoplastic, having a Shore D hardness of about 20 to about 70,more preferably about 30 to about 65 and most preferably about 35 toabout 60. A moisture vapor barrier layer, such as disclosed in U.S. Pat.Nos. 6,632,147; 6,932,720; 7,004,854; and 7,182,702, all of which areincorporated by reference herein in their entirety, are optionallyemployed between the cover layer and the core.

While any of the embodiments herein may have any known dimple number andpattern, a preferred number of dimples is 252 to 456, and morepreferably is 330 to 392. The dimples may comprise any width, depth, andedge angle disclosed in the prior art and the patterns may comprisesmultitudes of dimples having different widths, depths and edge angles.The parting line configuration of said pattern may be either a straightline or a staggered wave parting line (SWPL). Most preferably the dimplenumber is 330, 332, or 392 and comprises 5 to 7 dimples sizes and theparting line is a SWPL.

In any of these embodiments the single-layer core may be replaced with a2 or more layer core wherein at least one core layer has a negativehardness gradient.

Other than in the operating examples, or unless otherwise expresslyspecified, all of the numerical ranges, amounts, values and percentagessuch as those for amounts of materials and others in the specificationmay be read as if prefaced by the word “about” even though the term“about” may not expressly appear with the value, amount or range.Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and attached claims are approximationsthat may vary depending upon the desired properties sought to beobtained by the present invention. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical parameter should at least beconstrued in light of the number of reported significant digits and byapplying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Furthermore, when numerical ranges ofvarying scope are set forth herein, it is contemplated that anycombination of these values inclusive of the recited values may be used.While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objective stated above, it is appreciatedthat numerous modifications and other embodiments may be devised bythose skilled in the art. Therefore, it will be understood that theappended claims are intended to cover all such modifications andembodiments, which would come within the spirit and scope of the presentinvention.

1. A golf ball comprising a core and a cover, wherein the core comprisesa thermoset rubber composition, a geometric center and a treated outersurface, the treated outer surface having a first hardness and thegeometric center having a second hardness, the treated outer surfacebeing treated with a surface-softening material comprising at least onefatty acid and/or fatty acid salt plasticizer composition such that thesecond hardness is greater than the first hardness to define a negativehardness gradient.
 2. The golf ball of claim 1, wherein the thermosetrubber composition comprises a polybutadiene material having a surfacehardness of at least about 50 Shore C.
 3. The golf ball of claim 2,wherein the polybutadiene material is at least partially crosslinked. 4.The golf ball of claim 1, wherein the at least one fatty acid and/orfatty acid salt plasticizer composition comprises oleic acid, palmiticacid, stearic acid, behenic acid, pelargonic acid, linoleic acid,linolenic acid, arachidonic acid, caproic acid, caprylic acid, capricacid, lauric acid, erucic acid, myristic acid, benzoic acid,phenylacetic acid, or naphthalenoic acid.
 5. The golf ball of claim 4,wherein the at least one fatty acid and/or fatty acid salt plasticizercomposition comprises a cation selected from the group comprisingbarium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper,potassium, strontium, titanium, tungsten, magnesium, cesium, iron,nickel, silver, aluminum, tin and calcium.
 6. The golf ball of claim 1,wherein the at least one fatty acid and/or fatty acid salt plasticizercomposition further comprises antioxidants, sulfur-bearing compounds,zinc methacrylate, zinc dimethacrylate, softening acrylate monomers oroligomers, soft powdered thermoplastic resins, phenol-comprisingantioxidants, or hydroquinones.
 7. The golf ball of claim 6, wherein thesoft powdered thermoplastic resins comprise polyethylene vinyl acetate,polyethylene butyl acrylate, polyethylene methyl acrylate, orvery-low-modulus ionomer.
 8. The golf ball of claim 1, furthercomprising an outer core layer disposed about the core to form a dualcore comprising an untreated outer surface having a hardness.
 9. Thegolf ball of claim 1, further comprising an intermediate layer disposedabout the core and between the core and the cover layer.
 10. A golf ballcomprising a thermoset rubber composition core and a cover, said corecomprising a treated outer surface and a geometric center, the treatedouter surface comprising a fatty acid and/or fatty acid salt plasticizercomposition and extending inward from the surface from about 0.001inches to about 0.100 inches, the treated outer surface further having afirst hardness and the geometric center having a second hardness,wherein the first hardness is less than the second hardness to define anegative hardness gradient.